The present invention relates to the determination of an actuating force applied to a vehicle brake. The invention relates, in particular, to a vehicle brake that is capable of being actuated hydraulically and mechanically, and also to the determination of the actuating force generated in the case of joint hydraulic and mechanical actuation.
Hydraulic vehicle braking systems are increasingly being equipped with an electric parking brake (EPB). A braking system of such a type is known from DE 197 32 168 C2, and corresponding U.S. Pat. No. 6,394,235 B1, the disclosures of which are incorporated by reference herein in entirety, and comprises an electric drive motor, a gear mechanism and an actuating member in the form of a nut/spindle arrangement. The latter is provided for the purpose of translatorily moving a hydraulic piston of the hydraulic vehicle brake which is in contact with the nut/spindle arrangement. In this way, the hydraulic piston can be actuated mechanically without a hydraulic pressure on the hydraulic piston having to be built up. The actuating force exerted on the vehicle brake by the displacement of the hydraulic piston in this case is determined directly from the current consumption of the drive motor (i.e. without any force sensor).
The possibilities for application of the electric parking brake are not restricted only to the operation of a parking brake. By virtue of suitable mechanisms for control and regulation, the electric parking brake can be employed for the purpose of realizing further safety functions and comfort functions, such as, for example, a hill-start assistant (“hill-hold” function) or an emergency-brake assistant. The realization of such functions presupposes a coordinated interaction of electric parking brake and hydraulic-pressure generation. This, in turn, requires a coordinated monitoring and control of both systems.
Furthermore, it may be advantageous to assist the electric parking brake hydraulically during the generation of an actuating force (e.g. during a parking-brake procedure). However, this requires a precise determination and monitoring of the individual actuating-force components and of the resulting actuating force, in order to drive the electric parking brake and a hydraulic pressure generator appropriately, and in order to avoid malfunctions in the course of building up the actuating force.